Observations of vertical tidal motions of a floating iceberg in front of Shirase Glacier, East Antarctica, using a geodetic-mode GPS buoyObservations of vertical tidal motions of a floating iceberg in front of Shirase Glacier, East Antarctica, using a geodetic-mode GPS buoyObservations of vertical tidal motions of a floating iceberg in front of Shirase Glacier, East Antarctica, using a geodetic-mode GPS buoy

A dual-frequency GPS receiver was deployed on a floating iceberg downstream of the calving front of Shirase Glacier, East Antarctica, on 28 December 2011 for utilizing as floating buoy. The three-dimensional position of the buoy was obtained by GPS every 30 s with a 4–5-cm precision for ca. 25 days. The height uncertainty of the 1-h averaged vertical position was ∼0.5 cm, even considering the uncertainties of un-modeled ocean loading effects. The daily evolution of north–south (NS), east–west (EW), and up–down (UD) motions shows periodic UD variations sometimes attaining an amplitude of 1 m. Observed amplitudes of tidal harmonics of major constituents were 88%–93% (O1) and 85%–88% (M2) of values observed in the global ocean tide models FES2004 and TPXO-8 Atlas. The basal melting rate of the iceberg is estimated to be ∼0.6 m/day, based on a firn densification model and using a quasi-linear sinking rate of the iceberg surface. The 30-s sampling frequency geodetic-mode GPS buoy helps to reveal ice–ocean dynamics around the calving front of Antarctic glaciers.白瀬氷河カービングフロント付近の氷山上に測位用2周波GPS受信機を設置し、GPSブイとして活用した。その30秒毎の3次元位置を、精度4—5 cmで、約25日間測定した。平滑化した1時間毎の上下成分（0.5 cm程度の不確定性を持つ）は海洋潮汐による周期変動を示し、海洋潮汐解析で得られた主要分潮の振幅は、FES2004やTPXO-8 Atlas海洋潮汐モデルの88%–93%（O1分潮）や85%–88%（M2分潮）の値を持つ。氷山表面の沈降率とフィルン圧密モデルから、氷山底面の融解速度、0.6 m/dayが推定された。このように氷山を活用したGPSブイは、カービングフロント付近の氷・海洋ダイナミクスを明らかにするのに役立つ。